The invention relates to vaporizer burners in general, not only to those used in auxiliary heaters, but also e.g. for soot filter burners used for the elimination of soot residues. However, in the following, reference is made in particular to the subject of auxiliary heaters to illustrate the invention.
Especially in motor-independent auxiliary heaters running on liquid fuel for motor vehicles there are various kinds of heaters, e.g. burners operating with a pressure atomizer or a rotation atomizer. And there are vaporizer burners, in which the fuel is not atomized but vaporized for the generation of a fuel-air mixture. All the various burner types have certain advantages and disadvantages. In vaporizer burners the fuel is supplied to a vaporizer arrangement in a burner combustion chamber by means of a fuel dosing pump. This vaporizer arrangement comprises e.g. a kind of fiber packet or net, which fills out an area in the proximity of the glow plug for the starting of the burner. The fuel coming from the dosing pump is received by the fiber packet and reaches the flame area of a combustion chamber by means of capillary action. In order to initiate the combustion process, the glow plug is connected to a current source for a certain period of time. Furthermore, air is blown into the combustion chamber by means of combustion air blower. Basically the activation of the glow plug, the supplying of combustion air and the dosing of fuel can be started at the same time, usually, however, the pre-glowing takes place during the combustion air supply, and then the fuel is added. Due to the glow plug the vaporized fuel reaches the ignition temperature at the presence of air, so that the combustion process is started. After this starting process the glow plug is switched off.
It has been found that after the switching off of such vaporizer burners and during a later new starting of the heater blue smoke is generated. The after-exhaustion after the switching off of the vaporizer burner is the result of the extinguishing of the flame as the fuel supply is cut off, then the fuel remaining in the vaporizer arrangement is merely heated up, possibly while being supplied with combustion air during the usual after-running of the combustion air blower. Upon cutting the fuel supply a certain amount of fuel remains in the fiber packet of the vaporizer, and a part of it is turned into smoke once the flame is extinguished.
During the next start of the heater, especially during the pre-glowing and simultaneous supply of combustion air the fuel remainder in the fibre packet from the previous combustion process turns into smoke before new fuel is supplied and the fuel-air mixture is ignited.
The generation of blue smoke is undesirable with regard to the environment. A further disadvantage is that residues form in the area of the glow plug and the combustion chamber, which in time will impair the proper operation of the heater.